It is highly recommended that the DAT is completed as early as possible. Having a DAT score is not a requirement to submit the application. You can indicate that you plan to take it in the near future. To still be considered a moderately-early applicant, you should have your DAT done no later than July. You can take your exam later than that, but your application will lose its early advantage it had when you initially submitted it. Applications missing sections are put on hold until the section missing is received. I have heard of people taking the DAT as late as October or November of their application cycle!